Diffuse glioneuronal tumour with oligodendroglioma-like features and nuclear clusters (DGONC) - a molecularly defined glioneuronal CNS tumour class displaying recurrent monosomy 14.

AIMS: DNA methylation-based central nervous system (CNS) tumour classification has identified numerous molecularly distinct tumour types, and clinically relevant subgroups among known CNS tumour entities that were previously thought to represent homogeneous diseases. Our study aimed at characterizing a novel, molecularly defined variant of glioneuronal CNS tumour. PATIENTS AND METHODS: DNA methylation profiling was performed using the Infinium MethylationEPIC or 450 k BeadChip arrays (Illumina) and analysed using the 'conumee' package in R computing environment. Additional gene panel sequencing was also performed. Tumour samples were collected at the German Cancer Research Centre (DKFZ) and provided by multinational collaborators. Histological sections were also collected and independently reviewed. RESULTS: Genome-wide DNA methylation data from >25 000 CNS tumours were screened for clusters separated from established DNA methylation classes, revealing a novel group comprising 31 tumours, mainly found in paediatric patients. This DNA methylation-defined variant of low-grade CNS tumours with glioneuronal differentiation displays recurrent monosomy 14, nuclear clusters within a morphology that is otherwise reminiscent of oligodendroglioma and other established entities with clear cell histology, and a lack of genetic alterations commonly observed in other (paediatric) glioneuronal entities. CONCLUSIONS: DNA methylation-based tumour classification is an objective method of assessing tumour origins, which may aid in diagnosis, especially for atypical cases. With increasing sample size, methylation analysis allows for the identification of rare, putative new tumour entities, which are currently not recognized by the WHO classification. Our study revealed the existence of a DNA methylation-defined class of low-grade glioneuronal tumours with recurrent monosomy 14, oligodendroglioma-like features and nuclear clusters.

Utility of whole-exome sequencing for those near the end of the diagnostic odyssey: time to address gaps in care.

An accurate diagnosis is an integral component of patient care for children with rare genetic disease. Recent advances in sequencing, in particular whole-exome sequencing (WES), are identifying the genetic basis of disease for 25-40% of patients. The diagnostic rate is probably influenced by when in the diagnostic process WES is used. The Finding Of Rare Disease GEnes (FORGE) Canada project was a nation-wide effort to identify mutations for childhood-onset disorders using WES. Most children enrolled in the FORGE project were toward the end of the diagnostic odyssey. The two primary outcomes of FORGE were novel gene discovery and the identification of mutations in genes known to cause disease. In the latter instance, WES identified mutations in known disease genes for 105 of 362 families studied (29%), thereby informing the impact of WES in the setting of the diagnostic odyssey. Our analysis of this dataset showed that these known disease genes were not identified prior to WES enrollment for two key reasons: genetic heterogeneity associated with a clinical diagnosis and atypical presentation of known, clinically recognized diseases. What is becoming increasingly clear is that WES will be paradigm altering for patients and families with rare genetic diseases.

Changes in the expression profiles of claudins during gonocyte differentiation and in seminomas.

Testicular germ cell tumors (TGCTs) are the most common type of cancer in young men and their incidence has been steadily increasing for the past decades. TGCTs and their precursor carcinoma in situ (CIS) are thought to arise from the deficient differentiation of gonocytes, precursors of spermatogonial stem cells. However, the mechanisms relating failed gonocyte differentiation to CIS formation remain unknown. The goal of this study was to uncover genes regulated during gonocyte development that would show abnormal patterns of expression in testicular tumors, as prospective links between failed gonocyte development and TGCT. To identify common gene and protein signatures between gonocytes and seminomas, we first performed gene expression analyses of transitional rat gonocytes, spermatogonia, human normal testicular, and TGCT specimens. Gene expression arrays, pathway analysis, and quantitative real-time PCR analysis identified cell adhesion molecules as a functional gene category including genes downregulated during gonocyte differentiation and highly expressed in seminomas. In particular, the mRNA and protein expressions of claudins 6 and 7 were found to decrease during gonocyte transition to spermatogonia, and to be abnormally elevated in seminomas. The dynamic changes in these genes suggest that they may play important physiological roles during gonocyte development. Moreover, our findings support the idea that TGCTs arise from a disruption of gonocyte differentiation, and position claudins as interesting genes to further study in relation to testicular cancer.

Central nervous system atypical teratoid rhabdoid tumours: the Canadian Paediatric Brain Tumour Consortium experience.

BACKGROUND: Atypical teratoid rhabdoid tumours (ATRT) are aggressive brain tumours mostly occurring in early childhood. Largest published series arise from registries and institutional experiences (1-4). The aim of this report is to provide population-based data to further characterise this rare entity and to delineate prognostic factors. PATIENTS AND METHODS: A national retrospective study of children ⩽18years diagnosed with a central nervous system (CNS) ATRT between 1995 and 2007 was undertaken. All cases underwent central pathology review. RESULTS: There were 50 patients (31 males; median age at diagnosis of 16.7months). Twelve patients were >36months. Infratentorial location accounted for 52% of all cases. Nineteen patients (38%) had metastatic disease. Fifteen (30%) underwent gross total resection (GTR). Ten patients (20%) underwent palliation. Among the 40 remaining patients, 22 received conventional chemotherapy and 18 received high dose chemotherapy regimens (HDC); nine received intrathecal chemotherapy and 15 received adjuvant radiation. Thirty of the 40 treated patients relapsed/progressed at a median time of 5.5months (0-32). The median survival time of the entire cohort was 13.5months (1-117.5months). Age, tumour location and metastatic status were not prognostic. Patients with GTR had a better survival (2years overall survival (OS): 60%±12.6 versus 21.7%±8.5, p=0.03). HDC conferred better outcome (2years OS 47.9%±12.1 versus 27.3%±9.5, p=0.036). Upfront radiation did not provide survival benefit. Six of the 12 survivors (50%) did not receive radiation. CONCLUSION: The outcome of CNS ATRT remains poor. However, the use of HDC provides encouraging results. GTR is a significant prognostic factor. The role of adjuvant radiation remains unclear.

Duplication of 7q34 is specific to juvenile pilocytic astrocytomas and a hallmark of cerebellar and optic pathway tumours.

BACKGROUND: Juvenile pilocytic astrocytomas (JPA), a subgroup of low-grade astrocytomas (LGA), are common, heterogeneous and poorly understood subset of brain tumours in children. Chromosomal 7q34 duplication leading to fusion genes formed between KIAA1549 and BRAF and subsequent constitutive activation of BRAF was recently identified in a proportion of LGA, and may be involved in their pathogenesis. Our aim was to investigate additional chromosomal unbalances in LGA and whether incidence of 7q34 duplication is associated with tumour type or location. METHODS AND RESULTS: Using Illumina-Human-Hap300-Duo and 610-Quad high-resolution-SNP-based arrays and quantitative PCR on genes of interest, we investigated 84 paediatric LGA. We demonstrate that 7q34 duplication is specific to sporadic JPA (35 of 53 - 66%) and does not occur in other LGA subtypes (0 of 27) or NF1-associated-JPA (0 of 4). We also establish that it is site specific as it occurs in the majority of cerebellar JPA (24 of 30 - 80%) followed by brainstem, hypothalamic/optic pathway JPA (10 of 16 - 62.5%) and is rare in hemispheric JPA (1 of 7 - 14%). The MAP-kinase pathway, assessed through ERK phosphorylation, was active in all tumours regardless of 7q34 duplication. Gain of function studies performed on hTERT-immortalised astrocytes show that overexpression of wild-type BRAF does not increase cell proliferation or baseline MAPK signalling even if it sensitises cells to EGFR stimulation. CONCLUSIONS AND INTERPRETATION: Our results suggest that variants of JPA might arise from a unique site-restricted progenitor cell where 7q34 duplication, a hallmark of this tumour-type in association to MAPK-kinase pathway activation, potentially plays a site-specific role in their pathogenesis. Importantly, gain of function abnormalities in components of MAP-Kinase signalling are potentially present in all JPA making this tumour amenable to therapeutic targeting of this pathway.

Reduced in vitro functional activity of human NRAMP1 (SLC11A1) allele that predisposes to increased risk of pediatric tuberculosis disease.

Polymorphic variants within the human natural resistance-associated macrophage protein-1 (NRAMP1, also known as SLC11A1) gene have been shown to impact on susceptibility to tuberculosis in different human populations. In the mouse, Nramp1 is expressed at the macrophage phagosomal membrane and its activity can be assayed by the relative acquisition of mannose 6-phosphate receptor (M6PR) in Salmonella-containing vacuoles. Based on this M6PR recruitment assay, we have now developed an assay in primary human macrophages to test the function of human NRAMP1 gene variants. First, we established that M6PR acquisition was significantly higher (P = 0.002) in human U-937 monocytic cell lines transfected with NRAMP1 as compared to untransfected U-937 cells. Second, the M6PR assay was shown to be highly reproducible for NRAMP1 activity in monocyte-derived macrophages (MDM) from healthy volunteers. Finally, the assay was investigated in MDM from pediatric tuberculosis patients and significantly lower NRAMP1 activity was detected in MDM from individuals homozygous for the NRAMP1-274 high-risk allele (CC genotype) in comparison to heterozygous individuals (CT genotype; P=0.013). The present study describes both an assay for human NRAMP1 functional activity and concomitant evidence for reduced NRAMP1 function in the common genetic variant shown to be associated with tuberculosis susceptibility in pediatric patients.

Inhibition of medulloblastoma cell invasion by Slit.

Invasion of brain tumor cells has made primary malignant brain neoplasms among the most recalcitrant to therapeutic strategies. We tested whether the secreted protein Slit2, which guides the projection of axons and developing neurons, could modulate brain tumor cell invasion. Slit2 inhibited the invasion of medulloblastoma cells in a variety of in vitro models. The effect of Slit2 was inhibited by the Robo ectodomain. Time-lapse videomicroscopy indicated that Slit2 reduced medulloblastoma invasion rate without affecting cell direction or proliferation. Both medulloblastoma and glioma tumors express Robo1 and Slit2, but only medulloblastoma invasion is inhibited by recombinant Slit2 protein. Downregulation of activated Cdc42 may contribute to this differential response. Our findings reinforce the concept that neurodevelopmental cues such as Slit2 may provide insights into brain tumor invasion.

Impact of HLA matching on outcome of hematopoietic stem cell transplantation in children with inherited diseases: a single-center comparative analysis of genoidentical, haploidentical or unrelated donors.

SUMMARY: Hematological inherited diseases can be cured by hematopoietic stem cell transplantation (HSCT) from an human leukocyte antigen (HLA)-identical sibling donor (MSD), but the outcome of unrelated donors (URD) or haploidentical donors (HMD) has been a cause of concern. In all, 94 children affected with inherited diseases underwent HSCT at a single center using MSD (group A, n=31), URD (group B, n=23) or HMD (group C, n=40). There was no difference in the rate of engraftment or in the incidence of grades III-IV acute graft-versus-host disease (GVHD) between the groups. Survival rate was 80.6% in group A, 62.5% in group B and 47.5% in group C (P=0.023). In group B, survival rate was 73.7% in the subgroup with zero or one class I mismatch, and 25% in the subgroup with two or more class I mismatches (P=0.04). In group C, survival rate was 83.3% in the 9/10-identical subgroup, 64.3% in the seven or 8/10 subgroup, and 25% in the five or 6/10 subgroup (P=0.0007). Thus, engraftment, incidence of GVHD and survival are similar in recipients of grafts from MSD, URD with 0-1 class I-mismatch, or HMD with at least 7/10 HLA matches. The low success of HSCT using more disparate donors suggests reserving them for patients with very poor prognosis.

Lymphoproliferative disorders in children with primary immunodeficiencies: immunological status may be more predictive of the outcome than other criteria.

AIMS: Lymphoproliferative disorders (LPDs) are a severe complication in primary immunodeficiency and post-transplant patients. In primary immunodeficiency patients, LPDs are not well-known and, thus, we tried to evaluate their distinctive features and to determine prognostic factors predictive of clinical outcome by comparison with LPDs in post-transplant children. METHODS AND RESULTS: Clinical records and histopathology of 18 LPDs occurring in primary immunodeficieny children were compared with those of 10 LPDs in post-transplant children, together with results of in-situ hybridization for the detection of Epstein-Barr virus (EBV)-RNA and molecular biological techniques. LPDs were frequently extranodal, EBV-associated, and were more commonly pleomorphic in primary immunodeficiency than in post-transplant patients. A low T-cell count and abnormal T-cell function indicated bad prognosis in both groups. Polymorphic LPDs (PLPDs) were most frequent (n = 19), whereas lymphomas were rare (n = 7), and pseudo-tumoral lymphoid hyperplasias (n = 2) were observed only in primary immunodeficiency. Comparative p53/bcl-2 staining revealed a p53 overexpression in lymphomas compared with PLPDs; CD20/CD79a showed a similar staining in lymphomas, whereas PLPD expressed mainly CD20. TCR and IgH rearrangements did not help in distinguishing PLPDs from lymphomas, but detection of IgH clonality by Southern blot indicated poor prognosis, whereas oligoclonality by Southern blot regardless of PCR clonality and especially a polyclonal profile by Southern blot and PCR indicated a relatively good prognosis. CONCLUSIONS: This study documents the pleomorphism of LPDs in primary immunodeficiency compared to post-transplant children, even if some LPDs are similar in both groups (PLPDs). No criteria are useful enough to ascertain the diagnosis of malignancy in this series. Some molecular biological criteria help to predict the clinical outcome which, nevertheless, seems to depend more on the degree of immunosuppression and on T-lymphocyte presence and function.

Natural resistance to intracellular infections: natural resistance-associated macrophage protein 1 (Nramp1) functions as a pH-dependent manganese transporter at the phagosomal membrane.

Mutations at the natural resistance-associated macrophage protein 1 (Nramp1) locus cause susceptibility to infection with antigenically unrelated intracellular pathogens. Nramp1 codes for an integral membrane protein expressed in the lysosomal compartment of macrophages, and is recruited to the membrane of phagosomes soon after the completion of phagocytosis. To define whether Nramp1 functions as a transporter at the phagosomal membrane, a divalent cation-sensitive fluorescent probe was designed and covalently attached to a porous particle. The resulting conjugate, zymosan-FF6, was ingested by macrophages and its fluorescence emission was recorded in situ after phagocytosis, using digital imaging. Quenching of the probe by Mn(2+) was used to monitor the flux of divalent cations across the phagosomal membrane in peritoneal macrophages obtained from Nramp1-expressing (+/+) and Nramp1-deficient (-/-) macrophages. Phagosomes from Nramp1(+/+) mice extrude Mn(2+) faster than their Nramp(-/-) counterparts. The difference in the rate of transport is eliminated when acidification of the phagosomal lumen is dissipated, suggesting that divalent metal transport through Nramp1 is H(+) dependent. These studies suggest that Nramp1 contributes to defense against infection by extrusion of divalent cations from the phagosomal space. Such cations are likely essential for microbial function and their removal from the phagosomal microenvironment impairs pathogenesis, resulting in enhanced bacteriostasis or bactericidal activity.

Nramp 2 (DCT1/DMT1) expressed at the plasma membrane transports iron and other divalent cations into a calcein-accessible cytoplasmic pool.

Nramp2, also known as DMT1 and DCT1, is a 12-transmembrane (TM) domain protein responsible for dietary iron uptake in the duodenum and iron acquisition from transferrin in peripheral tissues. Nramp2/DMT1 produces by alternative splicing two isoforms differing at their C terminus (isoforms I and II). The subcellular localization, mechanism of action, and destination of divalent cations transported by the two Nramp2 isoforms are not completely understood. Stable CHO transfectants expressing Nramp2 isoform II modified by addition of a hemaglutinin epitope in the loop defined by the TM7-TM8 interval were generated. Immunofluorescence with permeabilized and intact cells established that Nramp2 isoform II is expressed at the plasma membrane and demonstrated the predicted extracytoplasmic location of the TM7-TM8 loop. Using the fluorescent, metal-sensitive dye calcein, and a combination of membrane-permeant and -impermeant iron chelators, Nramp2 transport was measured and quantitated with respect to kinetic parameters and at steady state. Iron transport at the plasma membrane was time- and pH-dependent, saturable, and proportional to the amount of Nramp2 expression. Iron uptake by Nramp2 at the plasma membrane was into the nonferritin-bound, calcein-accessible so-called "labile iron pool." Ion selectivity experiments show that Nramp2 isoform II can also transport Co(2+) and Cd(2+) but not Mg(2+) into the calcein-accessible pool. Parallel experiments with transfectants expressing the lysosomal Nramp1 homolog do not show any divalent cation transport activity, establishing major functional differences between Nramp1 and Nramp2. Monitoring the effect of Nramp2 on the calcein-sensisitve labile iron pool allows a simple, rapid, and nonisotopic approach to the functional study of this protein.

A new gene involved in DNA double-strand break repair and V(D)J recombination is located on human chromosome 10p.

V(D)J recombination, accountable for the diversity of T cell receptor- and immunoglobulin-encoding genes, is initiated by a lymphoid-specific DNA double-strand break. The general DNA repair machinery is responsible for the resolution of this break. Any defect in one of the known components of the DNA repair/V(D)J recombination machinery (Ku70, Ku80, DNA-PKcs, XRCC4 and DNA ligase IV) leads to abortion of the V(D)J rearrangement process, early block in both T and B cell maturation, and ultimately to severe combined immune deficiency (SCID) in several animal models. A human SCID condition is also characterized by an absence of mature T and B lymphocytes, and is associated with an increase in sensitivity to DNA-damaging agents (RS-SCID). None of the above-mentioned genes are defective in these patients, arguing for the likelihood of the existence of yet another unknown component of the V(D)J recombination/DNA repair apparatus. Athabascan-speaking (SCIDA) Navajo and Apache Native Americans have a very high incidence of T(-)B(-)SCID. The SCIDA locus is highly linked with markers on chromosome 10p, although the exact molecular defect has not been recognized in these patients. We show here that cells with the SCIDA defect are impaired in the DNA repair phase of V(D)J recombination similarly to RS-SCID, precisely an absence of V(D)J coding joint formation. Moreover, genotyping analysis in several RS-SCID families corroborates a linkage of the RS-SCID locus to the SCIDA region on chromosome 10p. These results demonstrate the presence of a new essential DNA repair/V(D)J recombination gene in this region, the mutation of which causes RS-SCID in humans.

Protein truncation test of LYST reveals heterogenous mutations in patients with Chediak-Higashi syndrome.

Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disorder in which an immune deficiency occurs in association with pigmentation abnormalities. Most patients who do not undergo bone marrow transplantation die of a lymphoproliferative syndrome, though some patients with CHS have a relatively milder clinical course of the disease. The large size of the LYST gene, defective in CHS, has made it difficult to screen for mutations in a large number of patients. Only 8 mutations have been identified so far, and all lead to a truncated LYST protein. We conducted protein truncation tests on this gene in 8 patients with CHS. Different LYST mutations were identified in all subjects through this approach, strengthening the observation of a high frequency of truncated LYST proteins as the genetic cause of CHS.

Early and prolonged intravenous immunoglobulin replacement therapy in childhood agammaglobulinemia: a retrospective survey of 31 patients.

OBJECTIVE: To evaluate the outcome of children who received prolonged intravenous immunoglobulin (IVIg) replacement therapy early in life for X-linked agammaglobulinemia (XLA). STUDY DESIGN: We performed a retrospective study of the clinical features and outcome of patients with genetic and/or immunologic results consistent with XLA. Patients receiving IVIg replacement therapy within 3 months of the diagnosis and for at least 4 years between 1982 and 1997 were included. RESULTS: Thirty-one patients began receiving IVIg replacement therapy at a median age of 24 months and were followed up for a median time of 123 months. IVIg was given at doses >0.25 g/kg every 3 weeks, and mean individual residual IgG levels ranged from 500 to 1140 mg/dL (median, 700 mg/dL). During IVIg replacement, the incidence of bacterial infections requiring hospitalization fell from 0.40 to 0.06 per patient per year (P <. 001). However, viral or unidentified infections still developed, including enteroviral meningoencephalitis (n = 3) causing death in one patient, exudative enteropathy (n = 3), and aseptic arthritis (n = 1). At last follow-up, 30 patients were alive at a median age of 144 months (range, 58 to 253 months). Among 23 patients who were evaluated by respiratory function tests and computed tomography, 3 had an obstructive syndrome, 6 had bronchiectasis, and 20 had chronic sinusitis. CONCLUSION: Early IVIg replacement therapy achieving residual IgG levels >500 mg/dL is effective in preventing severe acute bacterial infections and pulmonary insufficiency. More intensive therapy may be required to fully prevent the onset of bronchiectasis, chronic sinusitis, and nonbacterial infections, particularly enteroviral infections, in all cases.

Linkage of familial hemophagocytic lymphohistiocytosis to 10q21-22 and evidence for heterogeneity.

Familial hemophagocytic lymphohistiocytosis (FHL) is an autosomal recessive disorder characterized by the early onset of overwhelming activation of T lymphocytes and macrophages, invariably leading to death, in the absence of allogeneic bone marrow transplantation. Using genomewide genetic linkage analysis, we analyzed a group of 17 families with FHL and mapped a locus for FHL to the proximal region of the long arm of chromosome 10. Ten families showed no recombination with three tightly linked markers, D10S1650 (LOD score [Z]=6.99), D10S556 (Z=5.40), and D10S206 (Z=3.24), with a maximum multipoint LOD score of 11.22 at the D10S1650 locus. Haplotype analysis of these 10 families allowed us to establish D10S206 and D10S1665 as the telomeric and the centromeric flanking markers, respectively. Heterogeneity analysis and haplotype inspection of the remaining families confirmed that in seven families FHL was not linked to the 10q21-22 region, thus providing evidence for genetic heterogeneity of this condition.

Invasive pulmonary infection due to Scedosporium apiospermum in two children with chronic granulomatous disease.

Scedosporium apiospermum is an opportunistic fungus in humans. The incidence of S. apiospermum infection in patients with acquired neutropenia (e.g., patients receiving chemotherapy and bone marrow transplant recipients) is steadily increasing. S. apiospermum has poor in vitro susceptibility to "conventional" antifungal agents, rendering the management of infections complex. Patients with chronic granulomatous disease (CGD) are highly susceptible to fungal infections, which are mostly due to Aspergillus species. We describe two children with CGD and invasive pulmonary infection due to S. apiospermum. Both patients were treated with antifungal therapy including azole derivatives (itraconazole or voriconazole) and surgical resection of infected tissues. These cases highlight that scedosporium infection can closely mimic aspergillus infection and should be considered in any case in which there is a failure to respond to appropriate "conventional" antifungal therapy. We also suggest that the emergence of this pathogen may have been favored by long-term use of amphotericin B in both patients.

Prevention of EBV-induced B-lymphoproliferative disorder by ex vivo marrow B-cell depletion in HLA-phenoidentical or non-identical T-depleted bone marrow transplantation.

HLA-mismatched bone marrow transplantation (BMT) is hampered by three major complications: graft rejection, acute graft-versus-host disease (aGVHD) and delayed immune reconstitution. Infusion of anti-LFA1 plus anti-CD2 monoclonal antibodies (MAb), combined with ex-vivo T-cell depletion of the graft, was efficient in preventing graft rejection and aGVHD. Nevertheless, disease-free survival was limited by the high frequency of lethal infections, including EBV-induced lymphoproliferative disease (BLPD), which originates mostly from donor B cells, with an incidence of 5-30%. To decrease the rate of this complication, ex-vivo B-cell depletion was attempted. This study compares a group of 19 patients who received a T- and B-cell-depleted marrow from an HLA-mismatched related donor with a retrospective control group of 19 patients, who had received T-cell-depleted marrow by the same method. The level of T-cell depletion was similar in the two groups. For B-cell depletion, two different methods were compared. The median number of B cells infused in the study group was 0.46/kg. Engraftment and aGVHD incidence were similar in the two groups. No EBV donor-derived BPLD occurred in the study group, compared with seven in the control group, four of whom died because of EBV-BPLD. Event-free survival was significantly different between the two groups. We conclude that ex-vivo B-cell depletion of the graft may be a useful means of preventing EBV-BPLD, and warrants further study on a larger group of patients.

Ligands of CD4 inhibit the association of phospholipase Cgamma1 with phosphoinositide 3 kinase in T cells: regulation of this association by the phosphoinositide 3 kinase activity.

We have previously shown that CD4 ligands inhibit interleukin-2 (IL-2) production and T cell proliferation in human peripheral CD4+ T lymphocytes, in an MHC-independent way. Two major pathways implicated in T cell activation are inhibited by binding of CD4 ligands to the CD4 molecule, i.e. Ca2+ signaling by phospholipase Cgamma1 (PLCgamma1), and ERK-2 activation, suggesting a p21ras inhibition. We have correlated these inhibitions with the disruption of multifunctional complexes containing PLCgamma1, p120GAP and Sam68, induced by T cell activation. We report here that T cell activation through the TCR/CD3 induces an association of the phosphoinositide 3 kinase (PI3 kinase) with PLCgamma1, both in peripheral CD4+ T lymphocytes and the HUT-78 CD4+ T cell line. PI3 kinase is present in the multifunctional complexes that we have described previously. Preincubation of human peripheral CD4+ T cells and HUT-78 CD4+ T cells with gp160 or a peptide analogue of the HLA class II DR molecule precludes the association of PLCgamma1 with PI3 kinase. We also demonstrate, using two specific inhibitors of PI3 kinase activity (LY294002 and wortmannin), that this activity plays a key role in the association of PLCgamma1 with PI3 kinase. Moreover, we demonstrate the implication of the PI3 kinase activity in the negative signal mediated by HIV gp160 binding to CD4 molecules. We propose that the products of the PI3 kinase are important mediators of the negative signaling induced by the binding of CD4 ligands to the CD4 molecule implicated in the regulation of the formation of multifunctional complexes.